Method and device for detection and assessment of marijuana impairment

ABSTRACT

A method of identifying individuals impaired by a psychoactive substance such as cannabis. The method includes presenting monocularly to a subject being tested; to each eye separately, a sinusoidal grating pattern of fixed spatial frequency with achromatic contrast or color contrast between grating stripes being temporally alternately modulated at a temporal frequency that ranges between 10 Hz and 60 Hz with a pattern of the contrast being such that the subject being tested can see a frequency doubling in the grating pattern.

RELATED APPLICATION

This application is a continuation of application Ser. No. 15/297,886,filed Oct. 19, 2016, entitled “Impairment Measurement: Marijuana andDriving: Method and Device for Detection and Assessment of MarijuanaImpairment”, which claims the benefit of U.S. Provisional ApplicationNo. 62/243,933, filed Oct. 20, 2015, entitled “Impairment Measurement:Marijuana and Driving: Method and Device for Detection and Assessment ofMarijuana Impairment,” each of which is hereby fully incorporated hereinby reference.

FIELD OF THE INVENTION

The invention relates to testing for functional impairment arising fromthe consumption of cannabis and other psychoactive drugs. Moreparticularly the invention relates to testing for impairment caused bythe consumption of such substances to identify individuals who areimpaired for driving and other tasks.

BACKGROUND OF THE INVENTION

There are limited options available to detect impairments impactingdriving when impairment is due solely to cannabis use or the use ofother psychoactive drugs. In a 2007 roadside survey more drivers werepositive for drugs than alcohol (NHTS 2007) and this contributes to therisk of accidents when driving. Cannabis users suffer auto injury tentimes more frequently than non-users. (ScienceDaily) Eleven percent ofthose presenting in an emergency room after an auto accident were foundto have used cannabis in the absence of other drugs or alcohol and acutecannabis consumption presents a risk for motor vehicle crash and fatalcollisions involving motor vehicles. (Asbridge 2013)

A survey of drivers in Canada found that 4.8 percent of drivers admittedto driving within two hours of using cannabis. (Porath 2013) With thecurrent legalization of cannabis for recreational use in several states,the rate of automobile injury secondary to cannabis intoxication islikely to increase.

The state of Colorado has the most experience within the United States,with cannabis use and driving. Starting Jan. 1, 2014 Amendment 64 tookeffect allowing for the legal use of recreational cannabis in the stateof Colorado for citizens over the age of twenty one. Even though thelaws in Colorado clearly state that it is illegal to drive high, twelvepercent of the citations issued in 2014 for DUI involved cannabis use.The DUI fatality rate increased by 6 percent in 2014, and the rate ofDUI citations increased by 23 percent compared to 2013. Of the totalcitations issued, over six percent were suspected to involve onlycannabis and no other substances. Colorado officials take the positionthat any amount of cannabis can impair a person for driving and DUIcitations can be based on observations. Colorado has established a legallevel of cannabis that is considered to impair driving function at fivenanograms of active tetrahydrocannabinol, the component impactingcognitive function, per milliliter of whole blood. (Blood) Other stateshave adopted a zero tolerance level and there is research supportingthis that indicates how little cannabis is required to significantlyimpair skills required for driving. (Impair) The Colorado Department ofTransportation did a survey on the attitudes and behaviors of residentsseveral months before recreational cannabis became legal. They foundthat twenty percent of the respondents that had used cannabis in theprevious year had driven shortly after consuming cannabis and those thatdid so within two hours drove on average seventeen times during a month.(CDOTNEWS) Colorado invested one million dollars on a public educationcampaign, “Drive High, Get DUI”, in an effort to minimize the impact ofdriving while impaired secondary to cannabis. (Education) Even after thecampaign a survey found that 57% of those reporting to use cannabis,drove within two hours of consumption. (CDOT57)

Washington State has had legal marijuana for a shorter period, but stillis reporting significant problems with increasing numbers of impaireddrivers due to cannabis consumption. A report (Survey) for theWashington Traffic Safety Commission in a survey conducted by thePacific Institute for Research and Evaluation found that seventy percentof drivers questioned had used cannabis and of those reporting use 44%acknowledged they had driven a car less than two hours after usingcannabis. Further 90% of those who drove while using cannabis, did notfeel that cannabis impaired their ability to drive. In the year 2012there were 988 driver tests that came back positive for cannabis andthis increased to 1, 362 in 2013.(KXLY) From 2009 through 2013, morethan 1,000 people died in impaired driving collisions in Washington.Impaired driving is involved in nearly half of all traffic deaths andmore than 20 percent of serious injury collisions. (Kirkland) Whencannabis is combined with alcohol the effect is more deadly than alcoholalone. Alcohol intoxication increases the risk of a fatal accident bythirteen times compared to a sober driver but alcohol and cannabisintoxication increases the risk twenty four times. (Brady)

The National Institute on Drug Abuse prepared a White Paper on druggeddriving research in 2011 that discussed marijuana use; “For illegaldrugs, Zero Tolerance (ZT) per se laws are those which set that limit atthe drug detection cut-off level. In concept it is not necessary toprove driver impairment to convict an offender under a per se law.”(NIDA/Whitehouse} They further discussed per se drugged driving laws, “Aper se drugged driving law is one in which a specified level of a drugin the body of a driver is defined as an offense. This may be a level atwhich here is evidence that the drug has been shown to effect driverperformance such as the 0.08 g/mL limit for alcohol.”

There is limited research on cannabis impairment related to driving.Impairment due to cannabis differs significantly than the impairmentscaused by alcohol. Even small amounts detected in the blood have beenshown to impair the cognitive perceptual functions necessary for safedriving. (Zero). The demonstration of cognitive dysfunction even withsmall amounts of cannabis is fueling arguments for zero tolerance ofcannabis with driving. Fifteen states have zero tolerance regulationswhen it applies to drug use and cannabis. (Fifteen) While some excludemedical marijuana users, an estimated nine have more absolute laws withzero tolerance applied to all cannabis users.

In a September 2015 report from the Governor's Highway SafetyAdministration the complexities of evaluating impairment and drivingunder the influence of cannabis were discussed. Extraordinary attentionwas paid to cannabis as it is considered to be a threat to public healthsafety. The report reiterates that driving under the influence of drugs;DUID, is illegal in every state. This is much the same as driving underthe influence of alcohol, DUI. Like driving under the influence ofalcohol, DUID has two requirements that law enforcement must take intoconsideration. The driver must exhibit signs of impairment throughbehavior observed by a law enforcement officer and the impairment mustbe linked to a drug. An officer must have observed a driverdemonstrating impairment. Only then can an officer obtain chemicalevidence of a drug, usually through a blood test, and the officer mustbe able to link drug presence to the observed impairment. If the driverrefuses a blood test, the officer relies on observations. All this takeslonger than for alcohol. With alcohol use the signs are well understoodand backed by years of research. The Standardized Field Sobriety Testing(SFST) is an efficient and accurate screening. Evidence of blood alcohollevel can be obtained by the biomarkers present in a breath test. Thelinks between SFST, breath-testing and alcohol impairment are recognizedby the judiciary system. Traditional training of law enforcementofficers does not always include adequate training to observe impairmentto driving that arises from drugs. It can take several hours to obtainthe needed legal permissions to draw blood from a driver and there areconcerns that blood levels related to cannabis do not always match theimpairments. Further drug testing can be expensive with labs havingsubstantial backlogs. Cannabis related driving impairment presents aunique challenge to law enforcement as well as to the court systems. Aclear understanding of how cannabis has an impact on the ability todrive and limits on how an officer can compel further testing createsbarriers to removing drivers impaired by cannabis consumption from theroad. Unless there is evidence of impairment to drive similar to theSFST related to alcohol, an officer cannot require a driver to undergofurther evaluations.

When there is a concern related to impairment to drive, police officersuse standardized observation techniques. The most common is the SFST.The assessments used in the SFST were developed primarily to determinealcohol related impairment to drive. Currently assessments of the visualsystem by observation are part of a standardized field sobriety testsequence used to detect alcohol impairment. The standardized fieldsobriety test sequence is used to detect other impairments; includingcannabis.

A part of the SFST is the screening for alcohol related horizontal gazenystagmus. The horizontal gaze nystagmus related to alcohol occurs whenthe eyes move from looking straight ahead to the side in a horizontalmotion. The observation of a driver's eye movements along the horizontalaxis while the driver is fixating a target are subjectively interpretedfor the presence of horizontal nystagmus, jerking eye movement, and eyepursuit dysfunctions. If the nystagmus is observed to be present whenthe eye position is at an angle approximating forty five degrees or lessand/or there are losses of fixation during pursuit eye movements thereis a high likelihood that the driver has a blood alcohol level thatwould impair driving.

Horizontal gaze nystagmus testing has been shown to have an accuracy ofover 75% in the detection of blood alcohol content of 0.09% or greaterin a study undertaken by Dixon and colleagues. (Dixon 2009) Furthermore,studies of horizontal gaze nystagmus have shown the test to be sensitiveeven if blood alcohol levels are lower than legal limits of 0.08%.Horizontal gaze nystagmus testing, when properly administered issensitive in blood alcohol levels of 0.04-0.08%. (McKnight 2002) Thehorizontal nystagmus test is not complex to administer, but it doesrequire significant learned skill to interpret a driver's response. Thiscan create issues when presented in court as the officer'sadministration and interpretations of the test are subjective. When thesigns of horizontal gaze nystagmus occur, there is concern that theblood level is greater than 0.04%. (McKnight 2002) The rate of alcoholrelated auto accidents is staggering. Over 15,000 deaths associated withalcohol related traffic accidents occur annually, and over 40% of autofatalities each year are related to alcohol consumption. Cannabis alsoimpairs driving but, unlike alcohol, it is difficult to determine bloodlevels that cause impairment.

Application of eye movement as an indicator of impairment for cannabisuse is inconclusive. Citek and colleagues evaluated 25 participantsidentified by urinalysis to have cannabis as the only intoxicant andfound that there was lack of findings for deficits in eye movements.(Citek 2012) Adams and colleagues found deficits in horizontal gazenystagmus (HGN) as well as visual tracking with the consumption ofcannabis, but not at a level as significant as those seen withintoxication with alcohol. (Adams 1975) Smooth tracking eye movementsand saccadic tracking eye movements are reduced with alcohol but notwith marijuana or a placebo in the motion study undertaken by Flom andcolleagues. (Flom 1976) In a study of 20 adults using cannabis andcannabis combined with alcohol, researchers found that with cannabisalone the users showed impairment with the field sobriety test of oneleg stand, but dysfunctions in regards to horizontal gaze nystagmus werewhen cannabis was combined with alcohol. (Bosker 2012) Accordingly,horizontal gaze nystagmus appears not to be affected by cannabis eventhough affected by alcohol. One leg standing is uncertain as to itscorrelation with cannabis consumption.

There are products on the market to test for drug use. One theDrugTrap®, consists of a filter holder, mouthpiece, plastic bag withvolume indicators and seals for both ends. The consumer blows into themouthpiece and then the bag is sealed and mailed to the company foranalysis. The product is currently not FDA approved. (DrugTrap) Anotherproduct, though not on the market, is a telephone application to recordand analyze eye movement scanning with cannabis consumption. This isdescribed by Arizona State University Center for Innovation. (Arizona) Afurther product, BreathalEyes records eye movements and nystagmus andcalculates the probable blood alcohol content of the person using theapplication on a smart phone or tablet. (BreathalEyes) MyCanary is yetanother product. MyCanary is a telephone application that allows adriver to test their own theoretical potential to be too impaired todrive. It utilizes simple cognitive and physical tests includingbalance, memory, reaction and time perception and provides a readout forthe driver. There is no research or science background available on thisproduct and it is not intended to be used by law enforcement or thejustice system. (MyCanary)

Background on Retina and Brain Nuclei related to Cannabinoid Receptors

The active ingredients in cannabis act on cannabinoid receptors in thehuman body. The primary cannabinoid receptors that have been identifiedare classified as either CB1 or CB2 receptors. The CB2 category ishighly represented in the central nervous system; including the retina.CB2 receptors are represented in the central nervous system but to alesser degree than CB1 receptors. CB1 receptors have their greatestprevalence in the periphery and immune systems. In humans there are twoprimary endogenous compounds acting on the receptors,N-arachidonoylethanolamine (anandamide, AEA) and 2-arachidonoylglycerol(2-AG). Anandamide acts primarily post-synaptically as a retrogradecompound to modulate neurotransmitters. Anandamide has greater affinityfor CB1 receptors. 2-AG has been found to act pre-synaptically and alsohas greater affinity for CB1 receptors. 2-AG is found abundantly in thebrain, but shows less affinity for CB1 receptors than does Anandamide.(Shwitzer 2015) The receptor sites in the brain related to CB1 and CB2are primarily those involved in higher cognitive functions. Theforebrain, midbrain and hindbrain have areas associated with the controlof movement that are affected and hindbrain areas associated with thecontrol of motor and sensory functions of the autonomic nervous systemare affected. (Glass 1997) All regions where cannabinoid receptors havebeen identified have implications for performance related to driving.

The human retina has representation of cannabinoid receptors throughoutmultiple layers and cell structures. This is supported by animal models.CB1 activity in human retina is evidenced by staining in the synapticlayers of the retina; the inner and outer plexiform layers. The densityof CB1 Receptors increases in the inner nuclear layer and the ganglioncell layer. There is substantial staining in the outer segments of thephotoreceptors. (Straiker 1999) Research has demonstrated the expressionand regulation of CB1 receptors in human retinal pigment epitheliumcells. (Wei 2013) An animal model using mice supports this finding withidentification of CB1 receptors in the inner retina and ganglion cells,with integrations and processing of excitatory signal from bipolar cellsand inhibitory signals from amacrine cells. (Wang 2013) The activationof CB1 receptors differs dependent on the circadian quality of light;night versus daytime. If CB1 receptors are activated during day, therod-cone gap junctional signaling is decreased. However if activated atnight the rod-cone gap junctional signaling is increased. (Jieng ARVO)This has functional implications for scotopic vision and glare recovery.

An additional rodent model has demonstrated that CB2 receptors arelocalized in cone and rod photoreceptors, horizontal cells, someamacrine cells, and bipolar and ganglion cells. (Cecyre 2013) Additionalevidence of CB2 receptors within rodent retina as well as the centralnervous system has been identified by additional groups. (Hu 2010) Luand colleagues identified CB2 evidence in the somas of retina ganglioncells in a rodent model. (Lu 2000) This differs from a primate modelwhich shows that CB2 receptors are in the primate retina but exclusivelyin the retinal glia, with the model still supporting that CB1 receptorsare present in neuroretina. (Bouskilla 2013CB2)

One of the primary brain nuclei involved in processing visual signals isthe lateral geniculate nucleus (LGN) and this area of the brain is densein cannabinoid receptors. A primate model; the vervet monkey, shows thatCB1 receptors are located throughout the LGN with prominent findings inthe magnocellular layers. The receptors are less prominent, but stillevident, in the koniocellular layers. (Javadi 2015) Magnocellularfunctions involve primarily achromatic signals; related to contrast andtemporal functioning of vision. The currently used testing for glaucomautilizing contrast and temporal functioning is assessing magnocellularprocessing. Koniocellular functioning involves the processing ofchromatic signals in the blue wavelength. Another primate model of CB1functioning within the LGN shows demonstrated that the active ingredientin cannabis inhibits cells that would normally fire when exposed tolight and cells that would be inhibited by light were eitherunresponsive with no inhibition activity or actually had an increase inexcitation. (Bieger 1972) This has significant implications for theinteraction of central macular retinal functions and peripheral retinalfunctions as well as scotopic (night vision or dim light vision) andphotopic (daylight vision or bright light vision) functions.

DaSilva and colleagues were able to quantify the functional action onCB1 receptors within the LGN and found two populations; 28% were excitedby an antagonist and 72% were inhibited. When activated artificially (asthey would be with cannabis) the visual signals were altered. Withexcitatory activity there was a decrease in the signal to noise ratiobut an increase in variability. With altered inhibition; which accountsfor over seventy percent of the cells in the LGN, there was an increasein the signal to noise ratio with reductions in variability. Theresearchers concluded that the abnormal signals originating from the LGNwith artificial stimulation of the cannabinoid receptors using cannabisand then traveling to the cortex would account for the behavioraleffects of cannabis. (DaSilva 2012) The findings in the LGN supportevidence of diverse roles of cannabinoid receptors in both the retinaand the LGN, in modulating both excitation of cells and the inhibitorycell functions. The authors hypothesize that the cannabinoid receptorfunctions within the visual system account for many of the behavioraleffects from cannabis. The behavioral effects and changes in cognitivefunction along visual pathways, demonstrated by functional brainimaging, are enough to impair driving functions. (MRI) A rodent model ofdevelopment and function of CB1 receptors in the visual cortex foundintense staining for CB1 receptors in layers II, III, and VI. Thefunctions were influenced by dark and light cycling and had plasticityrelated to retinal stimulation. (Yoneda 2013)

Reductions in acuity have been reported secondary to cannabisconsumption. (Dawson 1977) Adams and colleagues did not find reductionsin static acuity but did find reductions in dynamic acuity aftercannabis consumption. (Adams 1975)

The structural findings related to the cones in the retina andkoniocellular layers of the LGN offer an explanation for the functionalfindings of color impairment with cannabis consumption. Severalresearchers have identified color deficits along the blue axis. Adamsand colleagues found dose related impairment with the consumption ofcannabis was identified using the Farnsworth-Munsell 100 hue test andthe findings were along the blue axis. The deficits were similar tothose blue deficits that occur with retinal based pathology leadingresearchers to conclude that the origin of the dysfunction was in theretina itself (Adams 1976) Dawson and colleagues supported the findingsof significantly reduced color vision functions with decreased colormatches among those having consumed cannabis. (Dawson 1977) In studiesof retinal tissue in vitro; Hu and colleagues found evidence ofcannabinoid function in postsynaptic cone bipolar cells that interactwith cone photoreceptors providing further physiologic evidence tosupport the functional deficits in color processing. (Hu 2010)

Early reports in the 1970s indicated that marijuana impacted pupillaryfunction with dose related constrictions of the pupil. (Hepler 1972,Brown 1977) More recent reports using pupilometer technology aredocumenting dose related dilations of the pupil. (Stark 2003, Merzouki2008) Dilated pupils as well a slow pupil reaction were reported to beindicators of cannabis consumption by Bramness and colleagues. Thediminished pupil reaction persisted for the first two hours. Theyobserved an increase in dilation among those with blood cannabisconcentrations above 2.9 ng/ml, but the observation was only present in35% of those consuming cannabis. (Bramness 2010)

There is evidence of dysfunction related to dark adaptation, lightadaptation, glare recovery and photopic functions with the consumptionof cannabis. (Dawson 1977, Adams 1978) This may be related to changes inpupil function, suppression of central inhibitory or excitatory retinalfunctions, abnormal retinal functions peripherally or any combination ofthe foregoing. The dysfunctions persist for two hours after cannabisconsumption. That cannabis impacts central photopic based functions isevidenced by studies that demonstrate increase in scotopic functions.There are reports of improved night vision with the use of cannabis.(Russo 2004) In support of increased peripheral scotopic function is thediscovery of a novel exogenous cannabinoid in rod segments and elsewherein the central nervous system of a primate model, GPR55. (Bouskilla2013GPR55)

There is room for improvement in the area of testing for functionalimpairment due to the consumption of cannabis and other psychoactivedrugs. There is currently no field applicable test available to identifythose driving impaired due cannabis consumption.

SUMMARY OF THE INVENTION

Example embodiments of the invention utilize retinal functioning as abiomarker for impairment to drive after consuming cannabis or otherdrugs. Embodiments of the invention, improve on existing strategies andprovides a practical field applicable test.

The technology of embodiments of the invention is a novel and quickpsychophysical visual assessment for the detection of functionalimpairment due to cannabis or other psychoactive drug consumption.Example embodiments of the invention include tests designed forprofessional administration and self-administration. Self-administeredtests may include the utility of vehicle ignition interlock applicationsto prevent an impaired person from operating a motor vehicle.

Current strategies to detect fitness to drive a vehicle or to operatemachinery include the observation of physical dysfunction in the form offield sobriety testing, and are usually performed by law enforcementpersonnel. The results of such testing correlate well with otherbiologic measures when the impairing substance is alcohol. Currentvehicle ignition interlock applications operate relative to detection ofalcohol only. No such device is known to exist for cannabis. Thecorrelation of field sobriety testing to biologic measures with othersubstances; marijuana and psychoactive drugs is poor. Marijuana, inparticular, and other psychoactive drugs impact additional cognitiveneuroprocesses that are crucial for the safe operation of a motorvehicle or the operation of machinery, that are not detectable with thephysical assessment using existing field sobriety testing.

The visual system is extensively involved in the cognitive functionsthat are essential for safe operation of a motor vehicle or machinery.The eye's retina has multiple levels of cellular activity that aremodulated by cannabis specific receptors as well as receptors specificto other psychoactive drugs. The consumption of cannabis, in particular,inhibits and alters cellular responses within the retina that rely onthe neural activity of cannabinoid receptors. A test as appliedaccording to embodiments of the invention specifically measures visualfunctions that are selectively inhibited by cannabinoid consumption orpathologically overstimulated by cannabis consumption. The test can alsoindirectly measure the effects of other psychoactive drugs. A testaccording to embodiments of the invention serves as a noninvasivebiomarker of functional cognitive impairment, measured through thevisual system, secondary to consumption of cannabis and otherpsychoactive drugs. Because the distribution of cannabinoid receptors isknown throughout the retina, the test parameters are sensitive andspecific to cellular functions impaired by cannabis.

The test, according to embodiments of the invention, is indirectlysensitive to other psychoactive drugs. Cognitive dysfunction and in thecase of this test; vision impairment, is an indicator of expectedimpairment that would interfere with safe driving or the operation ofmachinery. The test, according to embodiments of the invention, providesa noninvasive approach to quickly and accurately assess the functionalability to drive after consuming cannabis.

Example embodiments of the invention include a vision test utilizingachromatic or chromatic frequency doubling visual phenomena. Frequencydoubling phenomena are produced by either isoluminent pairs of colorvisual stimuli in the form of alternating stripes or achromatic visualstimuli in the form of contrasting alternating stripes. This testutilizes visual stimuli consisting of temporally alternating stripes ata rate of between 10 and 60 HZ in a grid series to induce a frequencydoubling pattern. The spatial frequency (width of the stripe) varies aswell as the temporal frequency (alternations per second) and contrast orsaturation. Chromatic stimuli include isoluminant, single wavelength,complementary color pairs, with the isoluminence and/or saturation beingvariable in that the pairs have variable luminance and/or saturationwhile remaining matched in luminence. The color pairs may include, forexample, blue and yellow or red and green. Isoluminence in this contextmeans that the colors are as close as practical to single wavelengthcolors.

Achromatic stimuli include pairs of achromatic stripes of variablecontrast between pairs. The stimuli are presented within the visualfield of each eye separately, one target presentation at a time with thelocation within the visual field varying from single target presentationto single target presentation, while the test subject fixates on a smallstationary fixation target. The presentation of stimuli are organized insuch a manner as to measure the appropriate visual field andfunctionality of visual field impaired by cannabis consumption or otherpsychoactive drugs, but not in a manner predictable to the test subject.

Stripes may be presented to the eye in a variety of orientations.According to example embodiments of the invention, stripes may bepresented peripherally to fixation in orientations parallel to meridiansof the eye, perpendicular to the meridians or oblique to the meridians.For the purposes of this disclosure meridians should be considered to belines that pass generally through the point of fixation or the fovea andthat radiate outwardly to the peripheral retina or peripheral visualfield.

Stripes may be presented parallel to the meridians of the eye with theintention of taking advantage of the meridional preference effect.Research has demonstrated that stimuli oriented radially, parallel tothe meridian, are better resolved than stimuli in other orientations.Accordingly, the eye may demonstrate greater sensitivity to stimuli withmeridionally oriented stripes.

Alternatively, if comparison between two striped stimuli is desired,example embodiments of the invention may present stripes at orientationsoblique to the ocular meridians. For example stimuli may be presented atangles of plus and minus forty five degrees relative to the meridians.This means that the two stimuli should be perceived with approximatelyequal sensitivity and facilitate comparison of the two stimuli.

Test strategies include threshold sensitivity as well as simpledetection. A test is presented to an individual on a personal type handheld electronic device such as hand held cellular phone or tablet or thelike. The test may also be presented on a head worn headset or eyeglasslike device as well. The headset may resemble a virtual reality typehead worn device and may be used in a situation where control of ambientlighting and brightness is beneficial. A test subject interacts with theelectronic device by triggering, for example, a momentary contact switchor a touch of the screen in response to seeing a test stimulus. Testpattern presentation strategy incorporates stimuli that measure bothfalse positive and false negative responses.

I. According to another example embodiment, the invention includes atechnology application test method to determine the impairment ordecreased function of the visual system secondary to cannabisconsumption or other psychoactive drugs. This example embodimentutilizes achromatic test patterns. That is black and white patterns. Anexample embodiment of the method includes multiple steps as follows:

-   -   A. Presenting monocularly to a subject being tested; in each eye        separately, an achromatic sinusoidal grating pattern (which is        seen by the subject as a pattern of stripes or alternately a        grid) of fixed spatial frequency with the contrast between        grating stripes being temporally modulated (alternations) at a        frequency that ranges between 10 Hz and 60 Hz with the pattern        of contrast being such that the subject being tested can see a        frequency doubling in the grating pattern.        -   1. Decreasing the contrast of the grating pattern presented            until a first contrast ratio/value is reached where the            frequency doubling in the grating pattern is no longer seen            by the test subject.        -   2. Further decreasing the contrast of the grating pattern            until the contrast ratio/value is well below the test            subject's threshold of detection of the ratio/value.        -   3. Increasing the contrast of the grating pattern until a            second contrast ratio/value is reached where the frequency            doubling in the grating pattern is first detectable.        -   4. Comparing the first contrast ratio/value and the second            contrast ratio/value to those of a normal population who            have not consumed cannabis and have no pathology impacting            the visual functions tested.        -   5. Taking the first contrast ratio/value identified in step            A1 and varying the temporal modulation (alterations) from 10            Hz to 60 Hz and determining when the frequency doubling in            the grating pattern is first detectable by the test subject.        -   6. Taking the second contrast ratio/value identified in step            A3 and varying the modulation (alterations) from 10 Hz to 60            Hz and determining when the frequency doubling in the            grating pattern is first detectable by the test subject.        -   7. Taking the values identified in (A1 through A5) and (A3            through A6) and comparing them to the contrast ratio values            combined with temporal values in the modulation            (alterations) and comparing them to those of a normal            population who have not consumed cannabis and have no            pathology impacting the functions tested.        -   8. A threshold is determined by a procedure based on            Bayesian statistics known as Zippy Estimation of Sequential            Testing (ZEST). ZEST uses techniques to combine prior            knowledge about the expected distribution of thresholds and            the initial probability density function using knowledge            obtained from each stimulus presentation. Studies have shown            that the advantages offered by this algorithm over other            strategies include a 50% reduced test time compared to other            threshold strategies, greater efficiency, and lower intra            and inter test variability.    -   B. Another example embodiment of the invention utilizes colored        test patterns and includes presenting monocularly to a subject        being tested; in each eye separately, a chromatic sinusoidal        grating pattern (stripes) with fixed spatial frequency and the        chromatic stripes being temporally modulated (alternations of        complementary stripes) at a frequency which ranges between 10 Hz        and 60 Hz with the pattern of saturation being such that the        subject being tested can see a frequency doubling in the        pattern. The colors of the chromatic sinusoidal grating pattern        are complementary colors with selection from the entire color        spectrum. The saturation of the chromatic stripes vary, but the        two pairs remain matched in luminence.        -   1. Decreasing the saturation of each complementary chromatic            pair (examples include: yellow and blue, red and green)            until a first saturation ratio/value is identified where the            frequency doubling is no longer seen by the test subject.        -   2. Further decreasing the saturation of the chromatic            grating pattern until the saturation ratio/value is well            below the test subject's threshold of detection of the            saturation ratio/value.        -   3. Increasing the saturation of the grating pattern until a            second saturation ratio/value is reached where the frequency            doubling in the grating pattern is first detectable.        -   4. Comparing the first saturation ratio/value and the second            saturation ration to those of a normal population who have            not consumed cannabis and have no pathology impacting the            visual functions tested.        -   5. Taking the values identified in step B1 from the multiple            chromatic pairs and varying the individual multiple            chromatic pairs temporal modulation (alterations) from 10 Hz            to 60 Hz and determining when the frequency doubling in the            grating pattern is first detectable to the test subject.        -   6. Taking the values identified in step B3 from the multiple            chromatic pairs and varying the individual multiple            chromatic pairs temporal modulation (alterations) from 10 Hz            to 60 Hz and determining when the frequency doubling in the            grating pattern is first detectable.        -   7. Taking the values identified in (B1 through B5) and (B3            through B6) and comparing them to the contrast ratio values            combined with temporal values in the modulation            (alterations) and comparing them to those of a normal            population who have not consumed cannabis and have no            pathology impacting the functions tested.        -   8. Threshold is determined by a procedure based on Bayesian            statistics known as ZEST as discussed above.    -   C. In further example embodiment, the application of steps A1-A8        and B1-B8 are performed while varying the spatial frequency of        the stripes.    -   D. In further example embodiment, a professionally administered        test has a fixed spatial frequency and a fixed temporal        frequency with the contrast or saturation being variable.    -   E. In further example embodiment, a self-administered test has a        fixed spatial frequency and a fixed temporal frequency with the        contrast or saturation being variable.    -   F. In further example embodiment, a self-administered test is        operably coupled to a vehicle ignition interlock device whereby        the vehicle is disabled if the test indicates impairment.        -   1. In further example embodiment, a self-administered test            operates in conjunction with a vehicle ignition interlock            application that has biometric recognition such as iris            recognition whereby the user driving the vehicle is            confirmed to be the test subject who has passed the test.            -   a. Biometric recognition limits the self-administration                of the test to only the operator designated or assigned                to the vehicle ignition interlock device.

It is clear that the aforementioned features, as well as those to bedescribed below, can be used not only in the combinations stated, butalso in other combinations or in isolation, without leaving the scope ofthis invention.

The above summary is not intended to describe each illustratedembodiment or every implementation of the subject matter hereof. Thefigures and the detailed description that follow more particularlyexemplify various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a test screen according to an exampleembodiment of the invention;

FIG. 2 is a depiction of a test screen according to another exampleembodiment of the invention;

FIG. 3 is a depiction of a test screen according to a further exampleembodiment of the invention; and

FIG. 4 is a schematic depiction of meridians of the eye or visual fieldand of gratings oriented parallel, perpendicular and oblique to themeridians.

DETAILED DESCRIPTION

Referring to FIGS. 1, 2 and 3, test screen 10 according to an exampleembodiment of the invention is depicted. Test screen 10 includesperimeter 12, background field 14, fixation target 16, first sine wavegrid 18 and second sine wave grid 20.

Background field 14 extends over the area within perimeter 12. Fixationtarget 16 is located approximately in the center of background field 14.Fixation target 16 may be any contrasting color to background field 14and may be steady or flashing in nature

First sine wave grid 18 and second sine wave grid 20 are representativeof test targets presented during testing according to an exampleembodiment of the invention. First sine wave grid 18 and second sinewave grid 20 are presented at random locations within background field14 peripheral to fixation target 16. The positions at which first sinewave grid 18 and second sine wave grid 20 are depicted represent twosuch random locations but many other random location are possible. Firstsine wave grid 18 and second sine wave grid 20 are presented incontrasting or complimentary colors including but not limited to, forexample, black and white, red and green or blue and yellow.

Background field 14 is generally uniform in color and intensity.According to an example embodiment, background filed 14 is yellow incolor but this should not be considered limiting.

Response input 22 is operably coupled to controller 24 and to testscreen 10. Response input 22 may be integrated into a touch screen ormay include a momentary contact switch operably y coupled to controller24. Test screen 10 may be presented on a handholdable digital devicesuch as a tablet, smartphone or a dedicated device. Controller 24 istypically included integrally in such a device and may include software,hardware or firmware including algorithms to operate the test.

According to a testing sequence of an example embodiment of theinvention, a test subject is presented with a screen to be viewed eitheron a hand held digital device or in a virtual reality like headset. Thesubject fixates central fixation target 16 such as a contrasting dot.First sine wave grid 18 and second sine wave grid 20 are presented atrandom locations within background field 14 peripheral to fixationtarget 16. Various additional sine wave grating targets (not depicted)are presented randomly at locations peripheral to central fixationtarget 16 in background field 14. The test subject responds when, forexample, first sine wave grid 18 is seen by activating response input22. Testing continues as described elsewhere in this application untilit is determined that the test subject is impaired or not impaired.

Ignition interlock 26 may be coupled to controller 24 and is operable asdiscussed elsewhere in this application.

Biometric identification device 28 may also be coupled to controller 24and is operable as discussed elsewhere in this application. Biometricidentification device 28 may include, for example, biometric irisrecognition, fingerprint recognition or biometric retinal recognition.

Referring to FIGS. 2 and 3, test screens according to other exampleembodiments are depicted.

Referring to FIG. 4, a schematic depiction of meridians of the eye orvisual field 29 and of gratings 30 oriented parallel, perpendicular andoblique to meridians 32.

Meridians 32 include superior meridian S, superior temporal meridian ST,temporal meridian T, inferior temporal meridian IT, inferior meridian I,inferior nasal meridian IN, nasal meridian N, and superior nasalmeridian SN.

Gratings 30 include meridian parallel gratings 34 and meridianperpendicular gratings 36 which are parallel or perpendicular to theirrespective meridians. Gratings 30 may also be presented as meridianoblique gratings 38.

Gratings 30 may be presented to the eye in a variety of orientations asdiscussed above. According to example embodiments of the invention,meridian parallel gratings 34 may be presented peripherally to fixationin orientations parallel to meridians 32, perpendicular to the meridiansor oblique to the meridians. For the purposes of this disclosuremeridians 32 should be considered to be lines that pass generallythrough point of fixation 40 and that radiate outwardly to theperipheral retina or peripheral visual field.

Gratings 30 may be presented parallel to meridians 32 with the intentionof taking advantage of the meridional preference effect. Research hasdemonstrated that stimuli oriented radially, parallel to the meridianlike meridian parallel gratings 34, are better resolved than stimuli inother orientations. Accordingly, the eye may demonstrate greatersensitivity to stimuli with meridian parallel gratings 34.

Alternatively, if comparison between two gratings 30 is desired, exampleembodiments of the invention may present meridian oblique gratings 38.For example meridian oblique gratings 38 may be presented at angles ofplus and minus forty five degrees relative to meridians 32. This meansthat meridian oblique gratings 38 should be perceived with approximatelyequal sensitivity and facilitate comparison of the two stimuli presentedby meridian oblique gratings 38.

Further aspects of embodiments of the invention are presented below.

1. A method of identifying individuals impaired by a psychoactivesubstance, the method comprising:

-   -   presenting monocularly to a subject being tested; to each eye        separately, a sinusoidal grating pattern of fixed spatial        frequency with achromatic contrast or color contrast between        grating stripes being temporally alternately modulated at a        temporal frequency that ranges between 10 Hz and 60 Hz with a        pattern of the contrast being such that the subject being tested        can see a frequency doubling in the grating pattern;    -   decreasing the contrast of the grating pattern presented until a        first contrast ratio/value is reached wherein the frequency        doubling in the grating pattern is no longer reported as being        seen by the test subject;    -   further decreasing the contrast of the grating pattern until a        second contrast ratio/value is well below the test subject's        threshold of detection of the second contrast ratio/value;    -   increasing the contrast of the grating pattern until a third        contrast ratio/value is reached where the frequency doubling in        the grating pattern is first detectable;    -   comparing the first contrast ratio/value and the third contrast        ratio/value to a range of expected values of a normal population        who have not consumed cannabis and have no pathology impacting        the visual functions tested;    -   if the first contrast ratio/value and the third contrast        ratio/value are within the expected range of values then        indicating that the test subject is not impaired; and    -   if the first contrast ratio/value and the third contrast        ratio/value are not within the expected range of values then        indicating that the test subject is impaired.

2. The method as claimed in claim 1, further comprising varying thefirst contrast ratio/value identified and varying the temporallyalternate modulation in a range from 10 Hz to 60 Hz and determining whenthe frequency doubling in the sinusoidal grating pattern is firstdetectable by the test subject.

3. The method as claimed in claim 1, further comprising varying thethird contrast ratio/value identified and varying the temporallyalternate modulation in a range from 10 Hz to 60 Hz and determining whenthe frequency doubling in the grating pattern is first detectable by thetest subject.

4. The method as claimed in claim 1, further comprising comparing thevalues identified in claims 1-3 above to the contrast ratio valuescombined with temporal values in the modulation (alterations) andcomparing them to those of a normal population who have not consumedcannabis and have no pathology impacting the functions tested.

5. The method as claimed in claimed in claim 1, further comprisingdetermining a threshold by a procedure based on Bayesian statisticsincluding Zippy Estimation of Sequential Testing (ZEST).

6. The method as claimed in claimed in claim 1, further comprisingpresenting the sinusoidal grating pattern achromatically.

7. The method as claimed in claim 1, further comprising presenting thesinusoidal grating pattern chromatically with alternate stripes being incomplementary colors.

8. The method as claimed in claim 7, wherein the complementary colorscomprise yellow and blue.

9. The method as claimed in claim 7, wherein the complementary colorsare matched in luminence.

10. The method as claimed in claim 8, wherein the sinusoidal gratingpattern is presented on a yellow background.

11. The method as claimed in claim 7, further comprising temporallyalternately modulating the contrast between grating stripes by varying asaturation of the stripes.

12. The method as claimed in claim 1, further comprising holding thespatial frequency and the temporal frequency fixed while varying thecontrast or saturation.

13. The method as claimed in claim 1, further comprising a vehicleignition interlock wherein if the test subject is found to be impairedthe vehicle ignition interlock prevents operation of a motor vehicle.

14. The method as claimed in claim 13, further comprising obtainingbiometric recognition wherein a user driving the vehicle is identifiedto be the test subject who took the test.

Various embodiments of systems, devices, and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the claimed inventions. It should beappreciated, moreover, that the various features of the embodiments thathave been described may be combined in various ways to produce numerousadditional embodiments. Moreover, while various materials, dimensions,shapes, configurations and locations, etc. have been described for usewith disclosed embodiments, others besides those disclosed may beutilized without exceeding the scope of the claimed inventions.

Persons of ordinary skill in the relevant arts will recognize that thesubject matter hereof may comprise fewer features than illustrated inany individual embodiment described above. The embodiments describedherein are not meant to be an exhaustive presentation of the ways inwhich the various features of the subject matter hereof may be combined.Accordingly, the embodiments are not mutually exclusive combinations offeatures; rather, the various embodiments can comprise a combination ofdifferent individual features selected from different individualembodiments, as understood by persons of ordinary skill in the art.Moreover, elements described with respect to one embodiment can beimplemented in other embodiments even when not described in suchembodiments unless otherwise noted.

Although a dependent claim may refer in the claims to a specificcombination with one or more other claims, other embodiments can alsoinclude a combination of the dependent claim with the subject matter ofeach other dependent claim or a combination of one or more features withother dependent or independent claims. Such combinations are proposedherein unless it is stated that a specific combination is not intended.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims, it is expressly intended thatthe provisions of 35 U.S.C. § 112(f) are not to be invoked unless thespecific terms “means for” or “step for” are recited in a claim.

1. (canceled)
 2. A method of identifying individuals impaired by apsychoactive substance other than alcohol, the method comprising:presenting monocularly to a subject being tested; to each eyeseparately, a pattern of fixed spatial frequency with achromaticcontrast between dark areas and light areas, the achromatic contrastbetween the dark areas and the light areas being temporally alternatelymodulated at a temporal frequency that ranges between 10 Hz and 60 Hzwith a pattern of the contrast being such that the subject being testedcan see a frequency doubling in the pattern thereby evaluating retinalfunction; decreasing the contrast of the pattern presented until a firstcontrast ratio/value is reached wherein the frequency doubling in thepattern is no longer reported as being seen by the test subject; furtherdecreasing the contrast of the pattern until a second contrastratio/value is below the test subject's threshold of detection of thesecond contrast ratio/value; increasing the contrast of the patternuntil a third contrast ratio/value is reached where the frequencydoubling in the pattern is first detectable; comparing the firstcontrast ratio/value and the third contrast ratio/value to a range ofexpected values of a normal population who have not consumed thepsychoactive substance and have no pathology impacting retinal visualfunctions tested; if the first contrast ratio/value and the thirdcontrast ratio/value are within the range of expected values, thenindicating that the test subject is not impaired; and if the firstcontrast ratio/value and the third contrast ratio/value are not withinthe range of expected values then indicating that the test subject isimpaired.
 3. The method as claimed in claim 2, further comprisingvarying the first contrast ratio/value identified and varying thetemporally alternate modulation in a range from 10 Hz to 60 Hz anddetermining a frequency doubling value when the frequency doubling inthe pattern is first detectable by the test subject.
 4. The method asclaimed in claim 2, further comprising varying the third contrastratio/value identified and varying the temporally alternate modulationin a range from 10 Hz to 60 Hz and determining a frequency doublingvalue when the frequency doubling in the pattern is first detectable bythe test subject.
 5. The method as claimed in claim 2, furthercomprising comparing the frequency doubling temporal value valuesidentified to the contrast ratio values combined with temporal values inthe modulation (alterations) and comparing the frequency doublingtemporal values to the temporal values of a normal population who havenot consumed the psychoactive substance and have no pathology effectingthe retinal visual_functions tested.
 6. The method as claimed in claim5, further comprising comparing the frequency doubling temporal valuevalues identified to the contrast ratio values combined with temporalvalues in the modulation (alterations) and comparing them to thetemporal values of a normal population who have not consumed thepsychoactive substance and have no pathology effecting the functionstested.
 7. The method as claimed in claimed in claim 2, furthercomprising determining a threshold by a procedure based on Bayesianstatistics including Zippy Estimation of Sequential Testing (ZEST). 8.The method as claimed in claimed in claim 2, further comprisingpresenting the pattern of fixed spatial frequency as an achromaticsinusoidal grating pattern.
 9. The method as claimed in claim 2, furthercomprising holding the spatial frequency and the temporal frequencyfixed while varying a contrast.
 10. The method as claimed in claim 2,further comprising using a vehicle ignition interlock wherein if thetest subject is found to be impaired the vehicle ignition interlockprevents operation of a motor vehicle.
 11. The method as claimed inclaim 14, further comprising obtaining biometric recognition wherein auser driving the vehicle is identified to be the test subject who tookthe test.
 12. The method as claimed in claim 8, further comprisingpresenting the sinusoidal grating patterns at an oblique angle to anocular meridian.
 13. The method as claimed in claim 8, furthercomprising presenting the sinusoidal grating patterns at a parallel orperpendicular to an ocular meridian.
 14. A device for identifyingindividuals impaired by a psychoactive substance other than alcohol, thedevice comprising: a display on which images are displayed monocularlyto a subject being tested; to each eye separately with achromaticcontrast between dark areas and light areas, the display presenting apattern of fixed spatial frequency with contrast between the dark andlight areas being temporally alternately modulated at a temporalfrequency that ranges between 10 Hz and 60 Hz with a pattern of thecontrast being such that the subject being tested can see a frequencydoubling in the pattern thereby evaluating retinal function; the displaybeing coupled to a processor that is programmed with an algorithm bywhich an operator can control the display to present the followingprocedure: decreasing the contrast of the pattern presented until afirst contrast ratio/value is reached wherein the frequency doubling inthe pattern is no longer reported as being seen by the test subject;further decreasing the contrast of the pattern until a second contrastratio/value is below the test subject's threshold of detection of thesecond contrast ratio/value; increasing the contrast of the patternuntil a third contrast ratio/value is reached where the frequencydoubling in the grating pattern is first detectable; comparing the firstcontrast ratio/value and the third contrast ratio/value to a range ofexpected values of a normal population who have not consumed thepsychoactive substance and have no pathology impacting the retinalvisual functions tested; if the first contrast ratio/value and the thirdcontrast ratio/value are within the range of expected values, thenindicating that the test subject is not impaired; and if the firstcontrast ratio/value and the third contrast ratio/value are not withinthe range of expected values then indicating that the test subject isimpaired.
 15. The device as claimed in claim 14, further comprising avehicle ignition interlock wherein if the test subject is found to beimpaired the vehicle ignition interlock prevents operation of a motorvehicle.
 16. The device as claimed in claim 14, further comprisingbiometric recognition wherein a user driving the vehicle is identifiedto be the test subject who took the test.